Romex is a brand name for a type of plastic insulated wire.
Sometimes called non-metallic sheath. The formal name is NM.
This is suitable for use in dry, protected areas (ie: inside
stud walls, on the sides of joists etc.), that are not subject
to mechanical damage or excessive heat. Most newer homes are
wired almost exclusively with NM wire. There are several
different categories of NM cable.
BX cable -- technically known as armored cable or "AC" has a
flexible aluminum or steel sheath over the conductors and is
fairly resistant to damage.
TECK cable is AC with an additional external thermoplastic
sheath.
Protection for cable in concealed locations: where NM or AC cable
is run through studs, joists or similar wooden members, the outer
surface of the cable must be kept at least 32mm/1.25" (CEC & NEC)
from the edges of the wooden members, or the cable should be protected
from mechanical injury. This latter protection can take the form of
metal plates (such as spare outlet box ends) or conduit.
[Note: inspector-permitted practice in Canada suggests that armored
cable, or flexible conduit can be used as the mechanical protection,
but this is technically illegal.]
Additional protection recommendations: [These are rules in the
Canadian codes. The 1993 NEC has many changes that bring
it close to these rules. These are reasonable answers to the
vague "exposed to mechanical damage" in both the NEC and CEC.]
- NM cable should be protected against mechanical damage
where it passes through floors or on the surface of walls
in exposed locations under 5 feet from the floor.
Ie: use AC instead, flexible conduit, wooden guards etc.
- Where cable is suspended, as in, connections to furnaces
or water heaters, the wire should be protected. Canadian
practice is usually to install a junction or outlet
box on the wall, and use a short length of AC cable
or NM cable in flexible conduit to "jump" to the appliance.
Stapling NM to a piece of lumber is also sometimes used.
- Where NM cable is run in close proximity to heating
ducts or pipe, heat transfer should be minimized by
means of a 25mm/1" air space, or suitable insulation
material (a wad of fiberglass).
- NM cable shall be supported within 300mm/1' of every box
or fitting, and at intervals of no more than 1.5m/5'.
Holes in joists or studs are considered "supports".
Some slack in the cable should be provided adjacent to
each box. [while fishing cable is technically in violation,
it is permitted where "proper" support is impractical]
- 2 conductor NM cable should never be stapled on edge.
[Knight also insists on only one cable per staple, referring
to the "workmanship" clause, but this seems more honoured
in the breach...]
- cable should never be buried in plaster, cement or
similar finish, except were required by code [Ie: cable
burial with shallow bedrock.].
- cable should be protected where it runs behind baseboards.
- Cable may not be run on the upper edge of ceiling joists
or the lower edges of rafters where the headroom is more
than 1m (39").
Whenever BX cable is terminated at a box with a clamp, small
plastic bushings must be inserted in the end of the cable to
prevent the clamps forcing the sharp ends of the armor through
the insulation.
Whenever BX cable is buried in thermal insulation, 90C
wire should be selected, but derated in current carrying
capacity to 60C.
BX is sometimes a good idea in a work shop unless covered by
solid wall coverings.
In places where damage is more likely (like on the back wall of
a garage ;-), you may be required to use conduit, a
UL- (or CSA-) approved metal pipe. You use various types of
fittings to join the pipe or provide entrance/exit for the
wire.
Service entrances frequently use a plastic conduit.
In damp places (eg: buried wiring to outdoor lighting) you will
need special wire (eg: CEC NMW90, NEC UF). NMW90 looks like
very heavy-duty NMD90. You will usually need short lengths of
conduit where the wire enters/exits the ground. [See underground
wiring section.]
Thermoplastic sheath wire (such as NM, NMW etc.) should not be
exposed to direct sunlight unless explicitly approved for that
purpose.
Many electrical codes do not permit the routing of wire through
furnace ducts, including cold air return plenums constructed
by metal sheeting enclosing joist spaces. The reason for this
is that if there's a fire, the ducting will spread toxic gasses
from burning insulation very rapidly through the building.
Teflon insulated wire is permitted in plenums in many areas.
Canada appears to use similar wire designations to the US,
except that Canadian wire designations usually include the
temperature rating in Celsius. Eg: "AC90" versus "AC".
In the US, NM-B is 90 degrees celcius.
NOTE: local codes vary. This is one of the items that changes
most often. Eg: Chicago codes require conduit *everywhere*.
There are very different requirements for mobile homes.
Check your local codes, *especially* if you're doing anything
that's the slightest out of the ordinary.
Wire selection table (incomplete - the real tables are enormous,
uncommon wire types or applications omitted)
Condition Type CEC NEC
Exposed/Concealed dry plastic NMD90 NM
armor AC90 AC
TECK90
Exposed/Concealed damp plastic NMD90 NMC
armor ACWU90
TECK90
Exposed/Concealed wet plastic NMWU90
armor ACWU90
TECK90
Exposed to weather plastic NMWU
TW etc.
armor TECK90
Direct earth burial/ plastic NMWU* UF
Service entrance RWU
TWU
armor RA90
TECK90
ACWU90
[* NMWU not for service entrance]

My daughter dropped a small necklace behind her dresser. The necklace crossed a plug terminal and shorted the receptacle.
I bought a new receptacle and installed the same. I still have no power I suspect there could be a bigger problem,this is aluminum wiring.
I've killed the breaker and call an electrician but am curious as to what happened.P.s. there is a dimmer switch on the same circuit.

Assuming you are installing two switches in a two switch box, you probably should have used 14/2 and 14/3 instead of replacing 14/2 with 12/2. If you are only installing one switch in a one switch box, you should only have one cable in the box.

I prefer to use nothing smaller than12 awg /the smallest sized wire on a circuit determines the allowable ampacity
Ex: 15 amp-14awg. 12awg-20amp only rule for thumb other factors such as continuous load,heating and others if you do not know the safe NEC rules then please call a qualified journeyman Electrician better be safe

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